MLS-C01 Exploratory Data Analysis Practice Question
An ML team is analyzing a time series dataset of daily website traffic. They notice a pattern where traffic spikes every Sunday. Which EDA technique should they use to confirm this seasonality?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Plot the time series data with a line plot
A line plot of time series data visually displays trends and repeating patterns, making it the most direct way to confirm weekly seasonality. Option B (autocorrelation) can quantify periodicity but is less intuitive for simple confirmation; it is not a histogram. Option C (scatter plot of traffic vs. day of week) aggregates data by day, losing the sequential order needed to see seasonality over time. Option D (histogram) shows value distribution, not time-dependent patterns.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Plot the time series data with a line plot
Why this is correct
A line plot over time directly reveals seasonal patterns.
- ✗
Compute autocorrelation at different lags
Why it's wrong here
Computing autocorrelation at different lags quantifies the linear correlation between the series and a delayed copy of itself, which can reveal repeating patterns. However, for a weekly spike every Sunday, the autocorrelation at lag 7 would be high, but the question asks for a technique to *confirm* seasonality, not merely detect a correlation value. The correct approach—decomposition or a seasonal subseries plot—visually isolates the weekly component and shows the Sunday peak directly against the day-of-week baseline. Autocorrelation is tempting because it is a standard tool for identifying periodicity in time series, and it would be correct if the goal were simply to measure the strength of the 7-day cycle rather than to confirm the specific day-of-week pattern.
- ✗
Create a scatter plot of traffic vs. day of week
Why it's wrong here
Scatter plot may show pattern but line plot is better for time series.
- ✗
Plot a histogram of the traffic values
Why it's wrong here
Histogram shows frequency distribution, not time patterns.
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